Generally, the two common forms of fluorescent lamps are the so-called "preheat" type and the "rapid-start" type. The preheat type of fluorescent lamp has heater current flow therethrough during lamp ignition and thereafter a voltage-sensitive starter, external of the lamp, opens and discontinues the above-mentioned heater current flow. However the "rapid-start" type of fluorescent lamp normally has current flow through each electrode not only during ignition but also during the operation period of the lamp. Thus, it can readily be seen that this continuous flow of heater current during operation of the rapid-start lamp is a cause for power loss in the system and an obvious and undesired cause for reduced operational efficiency.
In an effort to improve the energy efficiency of rapid-start fluorescent lamps, numerous suggestions and structural configurations have been suggested. For example, U.S. Pat. Nos. 4,052,687; 4,097,779; 4,114,968; 4,156,831; and 4,171,519 all of which are assigned to the assignee of the present application, provide numerous configurations for enhancing the operation of rapid-start fluorescent lamps. Primarily, each of the above-listed patents relates to rapid-start fluorescent lamps or bi-metal type circuit breakers for fluorescent lamps whereby heater current flow is discontinued during lamp operation.
Although each one of the above-listed structures and techniques enhances and provides numerous advantages over prior known configurations and processes, it has been found that problems still remain. More specifically, it has been found that the normal glass tubing, tubing having a wall thickness in the range of about 0.025 to 0.035-inch, ordinarily employed as the bulb for circuit breakers suited to rapid-start fluorescent lamps leaves much to be desired. For example, it has been found that an excessive amount of heat is required to form glass into a bulb when the glass has a wall thickness of about 0.025 to 0.035-inch. As a result of this heat, the lead wires and bi-metal strip associated with the thermally sensitive bi-metal switch type circuit breaker tend to undesirably oxidize. Also, a relatively large sealing capacity is required and an excessive amount of flushing gas must be employed in an effort to reduce the oxide formation on the electrical leads and bi-metal switch components, when glass having a relatively thick wall thickness is utilized.